1. Field of the Invention
The present invention relates to a magnetic recording medium in which recording layers are formed in a concavo-convex pattern on both sides of a substrate, a magnetic recording and reproducing apparatus provided with the same, a method for manufacturing the magnetic recording medium, and a method for checking the magnetic recording medium.
2. Description of the Related Art
Magnetic recording media such as hard disks which have recording layers on both sides of a substrate are now widely known. Such magnetic recording media are sectioned into data areas and servo areas, and the servo information for positioning a magnetic head and the like is recorded in the servo areas. The servo areas are radially positioned at appropriate intervals in a circumferential direction. The magnetic head is movable in an arc-shaped trajectory along the radial direction of the magnetic recording medium in close proximity to the surface of the magnetic recording medium, and each servo area is positioned in an arc-shape corresponding to the arc-shaped trajectory of the magnetic head. In the case of magnetic recording media having recording layers on both sides of the substrate, a magnetic head for the recording layer on one side and a magnetic head for the recording layer on the other side are arranged to move along a coaxial central axis. Accordingly, the shape of the servo areas in the recording layer on one side and the shape of the servo areas in the recording layer on the other side are plane-symmetric to each other and are therefore not the same.
The servo information refers to binary information, being “0” or “1” which is recorded on each magnetic domain corresponding to one bit of information by a predetermined servo pattern. In a conventional longitudinal recording medium, binary information of 0 or 1 is recorded by magnetizing each magnetic domain in one or the other circumferential direction. In perpendicular recording media, which have become increasingly widespread, binary information of 0 or 1 is recorded by magnetizing each magnetic domain in one or the other direction perpendicular to its surface.
In the step of recording servo information, the magnetic domains are magnetized one by one in accordance with the binary information of 0 or 1 for each magnetic recording medium. Hence, low productivity tends to be a problem. In particular, in recent years, with an increase in areal density and with a decrease in the head flying height accompanying the increase in areal density, high density and high precision recording is required even for the servo information. Therefore, there are growing demands to improve the recording efficiency of the servo information.
In view of the foregoing, a technique has been proposed in which, in a servo area, a recording layer is formed in only one of an area for recording binary information of 0 and an area for recording binary information of 1, and this recording layer is formed in the shape of a servo pattern (see, for example, Japanese Patent Application Laid-Open No. 2006-31855). In this manner, since the recording layer is magnetized so as to conform to the servo pattern by applying a direct current magnetic field uniformly to the magnetic recording medium, it is possible to substantially increase the recording efficiency of the servo information.
Meanwhile, a significant improvement in the areal density of magnetic recording media has been achieved by, for example, reducing the size of magnetic particles constituting a recording layer, changing materials, and improving the precision of head processing. A further increase in the areal density is expected in the future. However, problems such as the limit of magnetic head processing and the incorrect recording of information on a track adjacent to a target recording track due to the broadening of the recording magnetic field emanating from a magnetic head, crosstalk during reproduction have become apparent. Therefore, the improvement of the areal density by conventional improvement techniques has reached its limit.
Accordingly, as candidates for magnetic recording media in which a further improvement in the areal density can be achieved, discrete track media and patterned media have been proposed. In the discrete track media, a recording layer in a data area is formed in a concavo-convex pattern corresponding to the pattern of a track. In a patterned medium, a recording layer is formed in a concavo-convex pattern corresponding to the shape that divides a track in a circumferential direction.
When such discrete track media and patterned media are manufactured, the recording layer in a servo area can be processed into a concavo-convex pattern corresponding to a servo pattern in a process where the recording layer in the data area is processed into the concavo-convex pattern corresponding to the shape of the track or the like, and this is particularly advantageous in terms of productivity.
Using the methods of lithography and dry etching, which are used in the process of manufacturing a semiconductor, makes it possible to process the recording layer into the concavo-convex patterns that correspond to the track and the servo pattern.
However, since it appeared that one side of the magnetic recording medium had the same form as the other side thereof, this created a problem in the manufacturing process.
For example, since the manufacture of a magnetic recording medium in which the recording layer was formed in a concavo-convex pattern corresponding to the track pattern and the servo pattern, and which was not a continuous film, required high precision processing, it was preferable to control the precision of the deposition and etching of each layer forming the magnetic recording medium individually on one side and then the other side. However, it appeared as if one side of the magnetic recording medium had the same appearance as the other side, and as such, it was difficult to control the precision of the deposition and etching of each layer individually on one side and then the other side.
Moreover, since the shape of the servo area of the recording layer on one side and the shape of the servo area of the recording layer on the other side were plane-symmetric and were therefore not the same as described above, it was necessary to clearly distinguish one side of the magnetic recording medium from the other side thereof when installing the magnetic recording medium in a magnetic recording and reproducing device. However, since it appeared as if one side of the magnetic recording medium had the same appearance as the other side, this operation was not easy either.